ORIGINAL ARTICLE
Physical Capacity and Risk for Long-Term Sickness Absence A Prospective Cohort Study Among 8664 Female Health Care Workers Charlotte Diana Nørregaard Rasmussen, MSc, Lars Louis Andersen, PhD, Thomas Clausen, PhD, Jesper Strøyer, PhD, Marie Birk Jørgensen, PhD, and Andreas Holtermann, PhD
Objective: To assess the prospective associations between self-reported physical capacity and risk of long-term sickness absence among female health care workers. Methods: Female health care workers answered a questionnaire about physical capacity and were followed in a national register of sickness absence lasting for two or more consecutive weeks during 1-year follow-up. Using Cox regression hazard ratio analyses adjusted for age, smoking, body mass index, physical workload, job seniority, psychosocial work conditions, and previous sickness absence, we modeled risk estimates for sickness absence from low and medium physical capacity. Results: Low and medium aerobic fitness, low muscle strength, low flexibility, and low overall physical capacity significantly increased the risk for sickness absence with 20% to 34% compared with health care workers with high capacity. Conclusions: Low physical capacity increases the risk of long-term sickness absence among female health care workers.
T
he annual level of sickness absence in Denmark is 5%1 and has been stable on this level for the past 5 years.2 Such high prevalence of sickness absence constitutes a large economic burden for the society.3 Moreover, sickness absence is associated with enormous consequences for the individual such as permanent labor market detachment4 and early mortality.5,6 Sickness absence varies considerably between occupational groups.7,8 Sickness absence levels are particularly high in health care workers.9 Knowledge on risk factors for sickness absence among health care workers is therefore needed for developing more efficient preventive strategies. The high physical workload of health care workers encompassing frequent bending or twisting of the trunk and heavy lifting,10 as well as high physical exertion,11 is a well-known risk factor for sickness absence.12 Participatory ergonomics interventions have effectively reduced the physical workload among health care workers.13,14 Nevertheless, the effect on sickness absence from worksite physical activity interventions increasing physical capacity and thereby reducing the relative workload is lacking.15,16 A high physical capacity is suggested to be particularly important for being able to handle high physical work demands without being faced with increased risk for sickness absence.17 This notion is confirmed by one cross-sectional study18 and could be explained by workers with high physical capacity recovering faster after performing a physical task. For a worker with high physical capacity, a burden could be relatively lower compared with a worker with low physical capacity.19 It has, therefore, been suggested that studies ought to investigate the
From the National Research Centre for the Working Environment (Ms Rasmussen, Drs Andersen, Clausen, Jørgensen, and Holtermann), Copenhagen; and Administrative Headquarter of The Capital Region of Denmark (Dr Strøyer), Department of Financial affairs, Data Unit, Hillerød. Conflicts of Interest and Source of Funding: None declared. Address correspondence to: Charlotte Diana Nørregaard Rasmussen, MSc, National Research Centre for the Working Environment, Lersø Parkalle 105, DK 2100 Copenhagen Ø, Denmark ([email protected]). C 2015 by American College of Occupational and Environmental Copyright Medicine DOI: 10.1097/JOM.0000000000000395
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importance for sickness absence from factors related to handling the high physical workload.20 Previous studies have shown that health care workers generally have high physical work demands and low physical capacity.21 Therefore, it is conceivable that low physical capacity may be a particularly strong predictor for sickness absence among health care workers. Nevertheless, the risk from different types of physical capacity, for example, low aerobic fitness, low muscle strength, low balance, and low flexibility on sickness absence, is scarcely investigated as most studies investigate the effect of general physical activity.15 Nevertheless, one study by Faber and coworkers22 did not find that low muscle strength increases risk for long-term sickness absence. Tucker and coworkers23 found that higher aerobic fitness was associated with lower levels of sickness absence. Thus, to assess the need for initiating interventions improving physical capacity for reducing sickness absence among health care workers, it is needed to investigate if physical capacity is a risk factor for sickness absence in this population. In this study, physical capacity is assessed through selfreports in questionnaires. Self-reported physical capacity is shown to be valid for estimating aerobic fitness,24,25 muscle strength, and flexibility25 at group level. Self-reported physical capacity therefore provides a satisfactory measure of physical capacity for use in larger studies where objective measures on several thousand people are not feasible.24,25 The objective of this prospective cohort study was to investigate whether self-reported physical capacity, that is, aerobic fitness, balance, muscle strength, flexibility, and overall physical capacity, predicted risk for register-based long-term sickness absence among female health care workers in a 1-year follow-up period. We hypothesized that low physical capacity was associated with increased risk for long-term sickness absence.
METHODS Study Design and Participants A questionnaire survey on health and working conditions among employees in the eldercare services of 36 Danish municipalities was merged with a register of social transfer payments, the Danish Register for Evaluation of Marginalization (DREAM).26 The survey was conducted in 2004 to 2005 and included 12,744 employees. Of these potential respondents, 9947 completed a questionnaire, which yields a response rate of 78%. The respondents of the survey were identified by their unique personal identification number given to all Danish citizens at birth and followed in the DREAM register for 1 year after completion of the survey. Male respondents (N = 220) and respondents who were not directly engaged in the provision of care services (eg, kitchen staff, janitors, and administrators) (N = 995) were excluded from the analyses. Because of missing questionnaire replies (N = 68), the final data set consisted of data from 8664 responders.
Outcome Variable: Sickness Absence Data on sickness absence were obtained from the DREAM register,26,27 which contains weekly information on granted sickness JOEM r Volume 57, Number 5, May 2015
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Physical Capacity and Long-Term Sickness Absence
absence for all citizens in Denmark. Sickness absence compensation is given to the employer, who at the time of the study could apply for a refund from the state for employees after 2 weeks (ie, during the third week) of sickness absence. Thus, the DREAM register contains information on sickness absence periods of more than 2 consecutive weeks. In this study, we have decided to investigate the association between physical capacity and long-term sickness absence for absence periods lasting for more than 2 weeks because of this. Moreover, the municipal social security departments are obliged to initiate action plans for sickness absent persons after 8 weeks of absence. Thus, an additional analysis focusing on absence lasting 8 or more weeks was also conducted.
Risk Factor: Physical Capacity Physical capacity at baseline was self-rated on four visual analog scales with illustrations and verbal anchors for the extremes on muscle strength, flexibility, aerobic fitness, and balance, with 0 indicating the worst a person of my own age and sex can perform and 10 being the best a person of my own age and sex can perform. The subjects were asked (1) “How would you score your muscle strength compared with people of your own age and sex?”; (2) “How would you score your flexibility compared with people of your own age and sex?”; (3) “How would you score your aerobic fitness compared with people of your own age and sex?”; and (4) “How would you score your balance compared with people of your own age and sex?” The method has been proven reliable earlier among health care workers.25 A physical fitness index was made by combining muscle strength, flexibility, aerobic fitness, and balance. Then the physical capacities and the physical fitness index were stratified in three levels according to the distribution in the population. The group scoring “low” on each of the capacities approximates the lower quartile, the group scoring “medium” on each of the capacities approximates the two middle quartiles, and the group scoring “high” on each of the capacities approximates the higher quartile. The division into quartiles was used to make a bigger contrast between low and high physical capacities. The physical fitness index will be referred to as overall physical capacity. The classification can be seen in Tables 1 and 2.
Confounders Potential confounders included age, smoking status (smoker/nonsmoker), body mass index (kg/m2 ), job seniority, phys-
ical workload, psychosocial work conditions, and previous sickness absence. Physical workload was measured by the Hollman questionnaire asking about body postures of the trunk, positions of the arms, positions of the legs, and weight lifted during the working day.28 Responses to all questions were given on a five-point rating scale ranging from “never” to “very often.” Weight factors, based on the biomechanical model “The Dortmunder,”29 were then multiplied by the item scores of the corresponding body postures reported in the questionnaire and then added to an index of physical work load. Psychosocial work conditions were assessed by four scales from the Copenhagen Psychosocial Questionnaire.30 A previous analysis has shown that scales measuring emotional demands, role conflicts, influence at work, and quality of leadership predict longterm sickness absence in this study population,31 and, accordingly, we included these four scales as potential confounders (1) emotional demands (a four-item scale, sample item: “Is your work emotionally demanding?” Cronbach α = 0.81); (2) role conflicts (a four-item scale, sample item: “Are contradictory demands placed on you at work?” Cronbach α = 0.66); (3) influence at work (a four-item scale, sample item: “Do you have a large degree of influence concerning your work?” Cronbach α = 0.75); and (4) quality of leadership (a four-item scale, sample item: “To what extent would you say that your immediate superior gives high priority to job satisfaction?” Cronbach α = 0.89). Responses on the individual items were scored on five-point Likert scales with values ranging from 0 to 4. According to the manual, the scores were subsequently recoded into a scale ranging from 0 to 100, with 100 representing the highest degree of the measured dimension of the psychosocial work environment. Finally, we adjusted for sickness absence 1 year prior to baseline (defined as weeks 1 to 52 before replying to the baseline questionnaire).
STATISTICS Using the Cox proportional hazards model, we estimated hazard ratios (HR) and 95% confidence intervals (95% CI) of low and moderate (reference: high) physical capacity for onset of sickness absence during follow-up. The variables mentioned above were included in the analysis. Sickness absence during 1 year prior to baseline was entered as a dichotomous variable. Respondents were followed in the DREAM register for 1 year and censored after the first case of long-term sickness absence. Respondents were furthermore censored in case of retirement, immigration, or death. The
TABLE 1. Descriptive Statistics for Main Study Variables*
Age, yrs (mean, SD) Smokers (%) Body mass index (mean, SD) Physical workload (mean, SD) Job seniority, yrs (mean, SD) Emotional demands (mean, SD) Role conflicts (mean, SD) Influence at work (mean, SD) Quality of leadership (mean, SD) More than 2 wk sickness absence (%) More than 8 wk sickness absence (%)
Low Overall Physical Capacity (n = 1,694)
Medium Overall Physical Capacity (n = 4,736)
High Overall Physical Capacity (n = 2,234)
45 (9.99) 35 26 (5.11) 20 (9.99) 9 (7.34) 48 (18.47) 42 (15.16) 43 (20.38) 55 (21.89) 18 8
45 (10.03) 37 25 (4.33) 20 (9.80) 9 (7.27) 46 (18.10) 42 (15.46) 44 (20.14) 57 (21.42) 15 6
46 (9.96) 39 24 (3.60) 19 (10.23) 9 (7.27) 45 (19.28) 41 (16.39) 48 (21.45) 59 (22.37) 14 5
*Data are mean (SD) or %. SD, standard deviation.
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TABLE 2. Hazard Ratios (HR) and 95% Confidence Intervals (95% CI) for Onset of More Than 2 Weeks Sickness Absence or More Than 8 Weeks Sickness Absence During the 12 Months of Follow-up for Low (the Lower Quartile), Medium (Two Medium Quartiles), and High (Highest Quartile) Aerobic Fitness, Muscle Strength, Flexibility, Balance, and Overall Physical Capacity More Than 2 Weeks Sickness Absence
Low aerobic fitness (1–4) Medium aerobic fitness (5–6) High aerobic fitness (7–9) Low muscle strength (1–4) Medium muscle strength (5–6) High muscle strength (7–9) Low flexibility (1–4) Medium flexibility (4–6) High flexibility (7–9) Low balance (1–5) Medium balance (6–7) High balance (8–9) Low overall physical capacity (1–4.75) Medium overall physical capacity (5–6.67) High overall physical capacity (6.75–9)
More Than 8 Weeks Sickness Absence
n (%)
Model 1* HR (95% CI)
Model 2† HR (95% CI)
Model 1* HR (95% CI)
Model 2‡ HR (95% CI)
1,830 (21) 4,985 (58) 1,843 (21) 1,225 (14) 4,806 (56) 2,624 (30) 1,420 (16) 4,200 (49) 3,036 (35) 3,363 (39) 2,666 (31) 2,627 (30) 1,694 (19) 4,736 (55) 2,234 (26)
1.29 (1.07–1.57) 1.18 (1.00–1.39) 1 1.20 (1.00–1.44) 1.05 (0.92–1.19) 1 1.15 (0.97–1.36) 0.98 (0.86–1.12) 1 1.04 (0.90–1.19) 0.92 (0.79–1.07) 1 1.25 (1.05–1.49) 1.11 (0.96–1.28) 1
1.34 (1.10–1.62) 1.21 (1.03–1.42) 1 1.20 (1.00–1.44) 1.05 (0.92–1.19) 1 1.20 (1.02–1.43) 0.99 (0.87–1.13) 1 1.07 (0.93–1.23) 0.95 (0.82–1.11) 1 1.28 (1.07–1.52) 1.10 (0.96–1.27) 1
1.36 (1.01–1.82) 1.19 (0.93–1.53) 1 1.41 (1.07–1.86) 1.13 (0.92–1.39) 1 1.22 (0.95–1.58) 0.98 (0.80–1.21) 1 1.03 (0.83–1.28) 0.91 (0.72–1.14) 1 1.39 (1.06–1.82) 1.16 (0.92–1.45) 1
1.36 (1.01–1.83) 1.16 (0.90–1.49) 1 1.31 (0.99–1.73) 1.19 (0.97–1.47) 1 1.25 (0.96–1.61) 0.95 (0.77–1.16) 1 1.03 (0.83–1.28) 0.89 (0.71–1.13) 1 1.39 (1.06–1.82) 1.13 (0.90–1.42) 1
*Model 1: age, smoking, body mass index, physical workload, job seniority, and psychosocial work conditions. †Model 2: age, smoking, body mass index, physical workload, job seniority, psychosocial work conditions, and previous sickness absence (more than 2 weeks). ‡Model 2: age, smoking, body mass index, physical workload, job seniority, psychosocial work conditions, and previous sickness absence (more than 8 weeks).
estimation method was maximum likelihood, and the PHREG procedure of SAS 9.2 (SAS Institute, Cary, NC) was used.
RESULTS Table 1 shows the characteristics of the female health care workers divided into low, medium, and high overall physical capacity. Overall, of the 8664 persons who entered the study, 1382 were absent for more than 2 consecutive weeks in the 1-year follow-up period and 532 were absent for more than 8 consecutive weeks during followup. The percentages with sickness absence for more than 2 weeks range from 14% to 18% for low, medium, and high overall physical capacity, and the percentages for sickness absence for more than 8 weeks range from 5% to 8% for low, medium, and high overall physical capacity. Table 2 summarizes the risk estimates of long-term sickness absence. Health care workers who report low aerobic fitness, low muscle strength, and low overall physical capacity have a significantly increased risk of 18% to 29% for being absent for more than 2 consecutive weeks (model 1) compared with health care workers who report high aerobic fitness, high muscle strength, and high overall physical capacity. The risk for being absent for more than 2 consecutive weeks remained significantly increased for low aerobic fitness, low muscle strength, low flexibility, and low overall physical capacity compared with those with high levels of these physical capacities (model 2). Medium aerobic fitness significantly increased the risk for being absent for more than 2 consecutive weeks with 18% to 21% in both models referencing high aerobic fitness. No significant differences in risk for sickness absence were found from having a low or medium balance compared with having a high balance. The results of the additional analyses investigating the risk for being absent for more than 8 consecutive weeks in the follow-up period show that low aerobic fitness, low muscle strength, and low overall physical capacity significantly increased the risk of being absent with 36% to 41% (model 1) compared with high aerobic fitness, high muscle strength, and high overall physical capacity. In model 2, 528
with additional adjustment for previous sickness absence only low aerobic fitness and low overall physical capacity remained a significant risk factor for sickness absence for more than 8 consecutive weeks with 36% and 39%, respectively, compared with high aerobic fitness and high overall physical capacity. No significant risk of being absent for more than 8 consecutive weeks was found for having a low or medium balance or a low or medium flexibility compared with high balance and high flexibility.
DISCUSSION This study examined the association between physical capacity and risk of long-term sickness absence among female health care workers. The results of the study showed that low physical capacity generally increases the risk for long-term sickness absence among female health care workers. More specifically, low and medium aerobic fitness, low muscle strength, low flexibility, and low overall physical capacity increase the risk for being absent for more than 2 consecutive weeks. Moreover, low aerobic fitness and low overall physical capacity increase the risk for being absent for more than 8 consecutive weeks. This is in accordance with our hypothesis that low physical capacity generally is associated with increased risk for long-term sickness absence. The results of this study showing that low physical capacity is a risk factor for sickness absence are in agreement with previous cross-sectional analysis of physical capacity and sickness absence in male military personnel in Finland.18 Moreover, the results are in line with earlier studies reporting preventive effects on sickness absence from high levels of leisure time physical activity, normally leading to increased physical capacity.32,33 Already in 1969, Lind´en showed that absence from work could be influenced by a mismatch between physical capacity and physical work demands. Moreover, the author concluded that employees with subnormal physical capacity probably would not be able to handle strenuous physical work.34 For health care workers with low physical capacity, the high physical work demands might exceed the safety
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margin of the individual physical capacity and possibly lead to an impaired work ability35 and sickness absence.36 Future worksite interventions ought to investigate whether increasing physical capacity of health care workers with high physical work demands can prevent long-term sickness absence. But there is also a need to investigate whether physical training interventions improving physical capacity and thereby reducing the relative workload are more efficient than interventions with, for example, ergonomics reducing the workload. Besides investigating the association between physical capacity and long-term sickness absence, we also investigated the association with specific physical capacities. One of the most persistent risk factors in this study was low aerobic fitness, which significantly increased the risk for being absent for more than 2 consecutive weeks as well as being absent for more than 8 consecutive weeks with more than 29%. Moreover, medium aerobic fitness was also a significant risk factor for being absent for more than 2 consecutive weeks, but with slightly lower estimates (HR 1.18 and HR 1.21). This finding of a high aerobic fitness being protective against sickness absence has also been found in a previous study by Tucker and colleagues.23 Workplace interventions with aerobic training show limited evidence in improving aerobic fitness,37 and reviews on physical activity interventions at the workplace also show limited evidence of an effect on sickness absence. Nevertheless, the quality of the included studies were rated low in the reviews.15,37,38 Thus, there is a need for future high-quality studies investigating whether physical training interventions enhancing aerobic fitness can reduce long-term sickness absence among workers with high physical work demands. Low muscle strength was a significant risk factor for being absent for more than 2 consecutive weeks and tended to be so for being absent for more than 8 consecutive weeks (95% CI, 0.99 to 1.73). A previous prospective study found no association between low muscle strength and long-term sickness absence among a representative sample of workers.22 Nevertheless, an association between high physical work demands and low muscle strength has been found in previous research.39,40 Workplace interventions with strength training and coordination training41 have effectively improved muscle strength, but the effect on sickness absence was lacking.42 This makes it particularly important to investigate in high-quality studies whether increasing muscle strength among workers with high physical work demands is effective for preventing long-term sickness absence. In this study, we found the highest risks of long-term sickness absence when comparing low overall physical capacity with high overall physical capacity. We found a significant risk of 39% for being absent for more than 8 consecutive weeks and a risk of 28% for being absent for more than 2 consecutive weeks when comparing low overall physical capacity to high overall physical capacity. Thus, it seems important to not only focus on one specific physical capacity, that is, muscle strength, flexibility, or aerobic fitness, but also take the overall physical capacity into consideration. In an additional analysis that was not preplanned, we did an interaction analysis and found a significant interaction between physical workload and physical capacity (P < 0.05). Nevertheless, the results are difficult to interpret with large confidential intervals. Therefore, more studies with bigger sample sizes and protocol-based analyses are needed to give more conclusive results on this aspect. Overall, it seems that physical capacity is of importance for long-term sickness absence, and considering the major impact of sickness absence on society, employers, and employees, scientific evaluation of efforts toward increasing physical capacity among health care workers should be initiated.
Strengths and Limitations The study population of only female health care workers reduces the risk for confounding and bias from socioeconomic factors. Another strength is the ability to investigate associations between the
Physical Capacity and Long-Term Sickness Absence
physical capacity and risk of developing long-term sickness absence in a specific job group. A limitation of the study is the self-reported measure of exposures and covariates. It is not known whether differential misclassification of self-reported physical capacity may be associated with sickness absence. Nevertheless, the questions on physical capacity have been proven reliable earlier.23 In the applied register for sickness absence, the cause of the sickness absence is unknown. Moreover, we have no knowledge of changes in physical capacity or health issues that could affect the risk of sickness absence in the 1-year follow-up period.
CONCLUSIONS This study supports that low physical capacity increases the risk of long-term sickness absence among female health care workers. Therefore, future sickness absence interventions among health care workers having high physical work demands ought to include components increasing the physical capacity.
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Physical Capacity and Risk for Long-Term Sickness Absence A Prospective Cohort Study Among 8664 Female Health Care Workers Charlotte Diana Nørregaard Rasmussen, MSc, Lars Louis Andersen, PhD, Thomas Clausen, PhD, Jesper Strøyer, PhD, Marie Birk Jørgensen, PhD, and Andreas Holtermann, PhD
Objective: To assess the prospective associations between self-reported physical capacity and risk of long-term sickness absence among female health care workers. Methods: Female health care workers answered a questionnaire about physical capacity and were followed in a national register of sickness absence lasting for two or more consecutive weeks during 1-year follow-up. Using Cox regression hazard ratio analyses adjusted for age, smoking, body mass index, physical workload, job seniority, psychosocial work conditions, and previous sickness absence, we modeled risk estimates for sickness absence from low and medium physical capacity. Results: Low and medium aerobic fitness, low muscle strength, low flexibility, and low overall physical capacity significantly increased the risk for sickness absence with 20% to 34% compared with health care workers with high capacity. Conclusions: Low physical capacity increases the risk of long-term sickness absence among female health care workers.
T
he annual level of sickness absence in Denmark is 5%1 and has been stable on this level for the past 5 years.2 Such high prevalence of sickness absence constitutes a large economic burden for the society.3 Moreover, sickness absence is associated with enormous consequences for the individual such as permanent labor market detachment4 and early mortality.5,6 Sickness absence varies considerably between occupational groups.7,8 Sickness absence levels are particularly high in health care workers.9 Knowledge on risk factors for sickness absence among health care workers is therefore needed for developing more efficient preventive strategies. The high physical workload of health care workers encompassing frequent bending or twisting of the trunk and heavy lifting,10 as well as high physical exertion,11 is a well-known risk factor for sickness absence.12 Participatory ergonomics interventions have effectively reduced the physical workload among health care workers.13,14 Nevertheless, the effect on sickness absence from worksite physical activity interventions increasing physical capacity and thereby reducing the relative workload is lacking.15,16 A high physical capacity is suggested to be particularly important for being able to handle high physical work demands without being faced with increased risk for sickness absence.17 This notion is confirmed by one cross-sectional study18 and could be explained by workers with high physical capacity recovering faster after performing a physical task. For a worker with high physical capacity, a burden could be relatively lower compared with a worker with low physical capacity.19 It has, therefore, been suggested that studies ought to investigate the
From the National Research Centre for the Working Environment (Ms Rasmussen, Drs Andersen, Clausen, Jørgensen, and Holtermann), Copenhagen; and Administrative Headquarter of The Capital Region of Denmark (Dr Strøyer), Department of Financial affairs, Data Unit, Hillerød. Conflicts of Interest and Source of Funding: None declared. Address correspondence to: Charlotte Diana Nørregaard Rasmussen, MSc, National Research Centre for the Working Environment, Lersø Parkalle 105, DK 2100 Copenhagen Ø, Denmark ([email protected]). C 2015 by American College of Occupational and Environmental Copyright Medicine DOI: 10.1097/JOM.0000000000000395
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importance for sickness absence from factors related to handling the high physical workload.20 Previous studies have shown that health care workers generally have high physical work demands and low physical capacity.21 Therefore, it is conceivable that low physical capacity may be a particularly strong predictor for sickness absence among health care workers. Nevertheless, the risk from different types of physical capacity, for example, low aerobic fitness, low muscle strength, low balance, and low flexibility on sickness absence, is scarcely investigated as most studies investigate the effect of general physical activity.15 Nevertheless, one study by Faber and coworkers22 did not find that low muscle strength increases risk for long-term sickness absence. Tucker and coworkers23 found that higher aerobic fitness was associated with lower levels of sickness absence. Thus, to assess the need for initiating interventions improving physical capacity for reducing sickness absence among health care workers, it is needed to investigate if physical capacity is a risk factor for sickness absence in this population. In this study, physical capacity is assessed through selfreports in questionnaires. Self-reported physical capacity is shown to be valid for estimating aerobic fitness,24,25 muscle strength, and flexibility25 at group level. Self-reported physical capacity therefore provides a satisfactory measure of physical capacity for use in larger studies where objective measures on several thousand people are not feasible.24,25 The objective of this prospective cohort study was to investigate whether self-reported physical capacity, that is, aerobic fitness, balance, muscle strength, flexibility, and overall physical capacity, predicted risk for register-based long-term sickness absence among female health care workers in a 1-year follow-up period. We hypothesized that low physical capacity was associated with increased risk for long-term sickness absence.
METHODS Study Design and Participants A questionnaire survey on health and working conditions among employees in the eldercare services of 36 Danish municipalities was merged with a register of social transfer payments, the Danish Register for Evaluation of Marginalization (DREAM).26 The survey was conducted in 2004 to 2005 and included 12,744 employees. Of these potential respondents, 9947 completed a questionnaire, which yields a response rate of 78%. The respondents of the survey were identified by their unique personal identification number given to all Danish citizens at birth and followed in the DREAM register for 1 year after completion of the survey. Male respondents (N = 220) and respondents who were not directly engaged in the provision of care services (eg, kitchen staff, janitors, and administrators) (N = 995) were excluded from the analyses. Because of missing questionnaire replies (N = 68), the final data set consisted of data from 8664 responders.
Outcome Variable: Sickness Absence Data on sickness absence were obtained from the DREAM register,26,27 which contains weekly information on granted sickness JOEM r Volume 57, Number 5, May 2015
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Physical Capacity and Long-Term Sickness Absence
absence for all citizens in Denmark. Sickness absence compensation is given to the employer, who at the time of the study could apply for a refund from the state for employees after 2 weeks (ie, during the third week) of sickness absence. Thus, the DREAM register contains information on sickness absence periods of more than 2 consecutive weeks. In this study, we have decided to investigate the association between physical capacity and long-term sickness absence for absence periods lasting for more than 2 weeks because of this. Moreover, the municipal social security departments are obliged to initiate action plans for sickness absent persons after 8 weeks of absence. Thus, an additional analysis focusing on absence lasting 8 or more weeks was also conducted.
Risk Factor: Physical Capacity Physical capacity at baseline was self-rated on four visual analog scales with illustrations and verbal anchors for the extremes on muscle strength, flexibility, aerobic fitness, and balance, with 0 indicating the worst a person of my own age and sex can perform and 10 being the best a person of my own age and sex can perform. The subjects were asked (1) “How would you score your muscle strength compared with people of your own age and sex?”; (2) “How would you score your flexibility compared with people of your own age and sex?”; (3) “How would you score your aerobic fitness compared with people of your own age and sex?”; and (4) “How would you score your balance compared with people of your own age and sex?” The method has been proven reliable earlier among health care workers.25 A physical fitness index was made by combining muscle strength, flexibility, aerobic fitness, and balance. Then the physical capacities and the physical fitness index were stratified in three levels according to the distribution in the population. The group scoring “low” on each of the capacities approximates the lower quartile, the group scoring “medium” on each of the capacities approximates the two middle quartiles, and the group scoring “high” on each of the capacities approximates the higher quartile. The division into quartiles was used to make a bigger contrast between low and high physical capacities. The physical fitness index will be referred to as overall physical capacity. The classification can be seen in Tables 1 and 2.
Confounders Potential confounders included age, smoking status (smoker/nonsmoker), body mass index (kg/m2 ), job seniority, phys-
ical workload, psychosocial work conditions, and previous sickness absence. Physical workload was measured by the Hollman questionnaire asking about body postures of the trunk, positions of the arms, positions of the legs, and weight lifted during the working day.28 Responses to all questions were given on a five-point rating scale ranging from “never” to “very often.” Weight factors, based on the biomechanical model “The Dortmunder,”29 were then multiplied by the item scores of the corresponding body postures reported in the questionnaire and then added to an index of physical work load. Psychosocial work conditions were assessed by four scales from the Copenhagen Psychosocial Questionnaire.30 A previous analysis has shown that scales measuring emotional demands, role conflicts, influence at work, and quality of leadership predict longterm sickness absence in this study population,31 and, accordingly, we included these four scales as potential confounders (1) emotional demands (a four-item scale, sample item: “Is your work emotionally demanding?” Cronbach α = 0.81); (2) role conflicts (a four-item scale, sample item: “Are contradictory demands placed on you at work?” Cronbach α = 0.66); (3) influence at work (a four-item scale, sample item: “Do you have a large degree of influence concerning your work?” Cronbach α = 0.75); and (4) quality of leadership (a four-item scale, sample item: “To what extent would you say that your immediate superior gives high priority to job satisfaction?” Cronbach α = 0.89). Responses on the individual items were scored on five-point Likert scales with values ranging from 0 to 4. According to the manual, the scores were subsequently recoded into a scale ranging from 0 to 100, with 100 representing the highest degree of the measured dimension of the psychosocial work environment. Finally, we adjusted for sickness absence 1 year prior to baseline (defined as weeks 1 to 52 before replying to the baseline questionnaire).
STATISTICS Using the Cox proportional hazards model, we estimated hazard ratios (HR) and 95% confidence intervals (95% CI) of low and moderate (reference: high) physical capacity for onset of sickness absence during follow-up. The variables mentioned above were included in the analysis. Sickness absence during 1 year prior to baseline was entered as a dichotomous variable. Respondents were followed in the DREAM register for 1 year and censored after the first case of long-term sickness absence. Respondents were furthermore censored in case of retirement, immigration, or death. The
TABLE 1. Descriptive Statistics for Main Study Variables*
Age, yrs (mean, SD) Smokers (%) Body mass index (mean, SD) Physical workload (mean, SD) Job seniority, yrs (mean, SD) Emotional demands (mean, SD) Role conflicts (mean, SD) Influence at work (mean, SD) Quality of leadership (mean, SD) More than 2 wk sickness absence (%) More than 8 wk sickness absence (%)
Low Overall Physical Capacity (n = 1,694)
Medium Overall Physical Capacity (n = 4,736)
High Overall Physical Capacity (n = 2,234)
45 (9.99) 35 26 (5.11) 20 (9.99) 9 (7.34) 48 (18.47) 42 (15.16) 43 (20.38) 55 (21.89) 18 8
45 (10.03) 37 25 (4.33) 20 (9.80) 9 (7.27) 46 (18.10) 42 (15.46) 44 (20.14) 57 (21.42) 15 6
46 (9.96) 39 24 (3.60) 19 (10.23) 9 (7.27) 45 (19.28) 41 (16.39) 48 (21.45) 59 (22.37) 14 5
*Data are mean (SD) or %. SD, standard deviation.
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TABLE 2. Hazard Ratios (HR) and 95% Confidence Intervals (95% CI) for Onset of More Than 2 Weeks Sickness Absence or More Than 8 Weeks Sickness Absence During the 12 Months of Follow-up for Low (the Lower Quartile), Medium (Two Medium Quartiles), and High (Highest Quartile) Aerobic Fitness, Muscle Strength, Flexibility, Balance, and Overall Physical Capacity More Than 2 Weeks Sickness Absence
Low aerobic fitness (1–4) Medium aerobic fitness (5–6) High aerobic fitness (7–9) Low muscle strength (1–4) Medium muscle strength (5–6) High muscle strength (7–9) Low flexibility (1–4) Medium flexibility (4–6) High flexibility (7–9) Low balance (1–5) Medium balance (6–7) High balance (8–9) Low overall physical capacity (1–4.75) Medium overall physical capacity (5–6.67) High overall physical capacity (6.75–9)
More Than 8 Weeks Sickness Absence
n (%)
Model 1* HR (95% CI)
Model 2† HR (95% CI)
Model 1* HR (95% CI)
Model 2‡ HR (95% CI)
1,830 (21) 4,985 (58) 1,843 (21) 1,225 (14) 4,806 (56) 2,624 (30) 1,420 (16) 4,200 (49) 3,036 (35) 3,363 (39) 2,666 (31) 2,627 (30) 1,694 (19) 4,736 (55) 2,234 (26)
1.29 (1.07–1.57) 1.18 (1.00–1.39) 1 1.20 (1.00–1.44) 1.05 (0.92–1.19) 1 1.15 (0.97–1.36) 0.98 (0.86–1.12) 1 1.04 (0.90–1.19) 0.92 (0.79–1.07) 1 1.25 (1.05–1.49) 1.11 (0.96–1.28) 1
1.34 (1.10–1.62) 1.21 (1.03–1.42) 1 1.20 (1.00–1.44) 1.05 (0.92–1.19) 1 1.20 (1.02–1.43) 0.99 (0.87–1.13) 1 1.07 (0.93–1.23) 0.95 (0.82–1.11) 1 1.28 (1.07–1.52) 1.10 (0.96–1.27) 1
1.36 (1.01–1.82) 1.19 (0.93–1.53) 1 1.41 (1.07–1.86) 1.13 (0.92–1.39) 1 1.22 (0.95–1.58) 0.98 (0.80–1.21) 1 1.03 (0.83–1.28) 0.91 (0.72–1.14) 1 1.39 (1.06–1.82) 1.16 (0.92–1.45) 1
1.36 (1.01–1.83) 1.16 (0.90–1.49) 1 1.31 (0.99–1.73) 1.19 (0.97–1.47) 1 1.25 (0.96–1.61) 0.95 (0.77–1.16) 1 1.03 (0.83–1.28) 0.89 (0.71–1.13) 1 1.39 (1.06–1.82) 1.13 (0.90–1.42) 1
*Model 1: age, smoking, body mass index, physical workload, job seniority, and psychosocial work conditions. †Model 2: age, smoking, body mass index, physical workload, job seniority, psychosocial work conditions, and previous sickness absence (more than 2 weeks). ‡Model 2: age, smoking, body mass index, physical workload, job seniority, psychosocial work conditions, and previous sickness absence (more than 8 weeks).
estimation method was maximum likelihood, and the PHREG procedure of SAS 9.2 (SAS Institute, Cary, NC) was used.
RESULTS Table 1 shows the characteristics of the female health care workers divided into low, medium, and high overall physical capacity. Overall, of the 8664 persons who entered the study, 1382 were absent for more than 2 consecutive weeks in the 1-year follow-up period and 532 were absent for more than 8 consecutive weeks during followup. The percentages with sickness absence for more than 2 weeks range from 14% to 18% for low, medium, and high overall physical capacity, and the percentages for sickness absence for more than 8 weeks range from 5% to 8% for low, medium, and high overall physical capacity. Table 2 summarizes the risk estimates of long-term sickness absence. Health care workers who report low aerobic fitness, low muscle strength, and low overall physical capacity have a significantly increased risk of 18% to 29% for being absent for more than 2 consecutive weeks (model 1) compared with health care workers who report high aerobic fitness, high muscle strength, and high overall physical capacity. The risk for being absent for more than 2 consecutive weeks remained significantly increased for low aerobic fitness, low muscle strength, low flexibility, and low overall physical capacity compared with those with high levels of these physical capacities (model 2). Medium aerobic fitness significantly increased the risk for being absent for more than 2 consecutive weeks with 18% to 21% in both models referencing high aerobic fitness. No significant differences in risk for sickness absence were found from having a low or medium balance compared with having a high balance. The results of the additional analyses investigating the risk for being absent for more than 8 consecutive weeks in the follow-up period show that low aerobic fitness, low muscle strength, and low overall physical capacity significantly increased the risk of being absent with 36% to 41% (model 1) compared with high aerobic fitness, high muscle strength, and high overall physical capacity. In model 2, 528
with additional adjustment for previous sickness absence only low aerobic fitness and low overall physical capacity remained a significant risk factor for sickness absence for more than 8 consecutive weeks with 36% and 39%, respectively, compared with high aerobic fitness and high overall physical capacity. No significant risk of being absent for more than 8 consecutive weeks was found for having a low or medium balance or a low or medium flexibility compared with high balance and high flexibility.
DISCUSSION This study examined the association between physical capacity and risk of long-term sickness absence among female health care workers. The results of the study showed that low physical capacity generally increases the risk for long-term sickness absence among female health care workers. More specifically, low and medium aerobic fitness, low muscle strength, low flexibility, and low overall physical capacity increase the risk for being absent for more than 2 consecutive weeks. Moreover, low aerobic fitness and low overall physical capacity increase the risk for being absent for more than 8 consecutive weeks. This is in accordance with our hypothesis that low physical capacity generally is associated with increased risk for long-term sickness absence. The results of this study showing that low physical capacity is a risk factor for sickness absence are in agreement with previous cross-sectional analysis of physical capacity and sickness absence in male military personnel in Finland.18 Moreover, the results are in line with earlier studies reporting preventive effects on sickness absence from high levels of leisure time physical activity, normally leading to increased physical capacity.32,33 Already in 1969, Lind´en showed that absence from work could be influenced by a mismatch between physical capacity and physical work demands. Moreover, the author concluded that employees with subnormal physical capacity probably would not be able to handle strenuous physical work.34 For health care workers with low physical capacity, the high physical work demands might exceed the safety
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margin of the individual physical capacity and possibly lead to an impaired work ability35 and sickness absence.36 Future worksite interventions ought to investigate whether increasing physical capacity of health care workers with high physical work demands can prevent long-term sickness absence. But there is also a need to investigate whether physical training interventions improving physical capacity and thereby reducing the relative workload are more efficient than interventions with, for example, ergonomics reducing the workload. Besides investigating the association between physical capacity and long-term sickness absence, we also investigated the association with specific physical capacities. One of the most persistent risk factors in this study was low aerobic fitness, which significantly increased the risk for being absent for more than 2 consecutive weeks as well as being absent for more than 8 consecutive weeks with more than 29%. Moreover, medium aerobic fitness was also a significant risk factor for being absent for more than 2 consecutive weeks, but with slightly lower estimates (HR 1.18 and HR 1.21). This finding of a high aerobic fitness being protective against sickness absence has also been found in a previous study by Tucker and colleagues.23 Workplace interventions with aerobic training show limited evidence in improving aerobic fitness,37 and reviews on physical activity interventions at the workplace also show limited evidence of an effect on sickness absence. Nevertheless, the quality of the included studies were rated low in the reviews.15,37,38 Thus, there is a need for future high-quality studies investigating whether physical training interventions enhancing aerobic fitness can reduce long-term sickness absence among workers with high physical work demands. Low muscle strength was a significant risk factor for being absent for more than 2 consecutive weeks and tended to be so for being absent for more than 8 consecutive weeks (95% CI, 0.99 to 1.73). A previous prospective study found no association between low muscle strength and long-term sickness absence among a representative sample of workers.22 Nevertheless, an association between high physical work demands and low muscle strength has been found in previous research.39,40 Workplace interventions with strength training and coordination training41 have effectively improved muscle strength, but the effect on sickness absence was lacking.42 This makes it particularly important to investigate in high-quality studies whether increasing muscle strength among workers with high physical work demands is effective for preventing long-term sickness absence. In this study, we found the highest risks of long-term sickness absence when comparing low overall physical capacity with high overall physical capacity. We found a significant risk of 39% for being absent for more than 8 consecutive weeks and a risk of 28% for being absent for more than 2 consecutive weeks when comparing low overall physical capacity to high overall physical capacity. Thus, it seems important to not only focus on one specific physical capacity, that is, muscle strength, flexibility, or aerobic fitness, but also take the overall physical capacity into consideration. In an additional analysis that was not preplanned, we did an interaction analysis and found a significant interaction between physical workload and physical capacity (P < 0.05). Nevertheless, the results are difficult to interpret with large confidential intervals. Therefore, more studies with bigger sample sizes and protocol-based analyses are needed to give more conclusive results on this aspect. Overall, it seems that physical capacity is of importance for long-term sickness absence, and considering the major impact of sickness absence on society, employers, and employees, scientific evaluation of efforts toward increasing physical capacity among health care workers should be initiated.
Strengths and Limitations The study population of only female health care workers reduces the risk for confounding and bias from socioeconomic factors. Another strength is the ability to investigate associations between the
Physical Capacity and Long-Term Sickness Absence
physical capacity and risk of developing long-term sickness absence in a specific job group. A limitation of the study is the self-reported measure of exposures and covariates. It is not known whether differential misclassification of self-reported physical capacity may be associated with sickness absence. Nevertheless, the questions on physical capacity have been proven reliable earlier.23 In the applied register for sickness absence, the cause of the sickness absence is unknown. Moreover, we have no knowledge of changes in physical capacity or health issues that could affect the risk of sickness absence in the 1-year follow-up period.
CONCLUSIONS This study supports that low physical capacity increases the risk of long-term sickness absence among female health care workers. Therefore, future sickness absence interventions among health care workers having high physical work demands ought to include components increasing the physical capacity.
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